Metallurgists... is There a COR-TEN Steel Sealant?

Unfortunately too big to bake. But that would have been good.

The clear-coat is very interesting though. Of course I'd thought of clear coat... but I rejected it due to the shinyness. But the buffing part... now that sounds very intrigueing and out-of-boxish. I like it. I will be looking into that.

The #0000 might give you the most uniform finish, buff in overlapping circular motion. Just make sure to wipe it down or wash it afterwards so you don't leave behind exposed particles of steel from the steel wool.

There are various abrasives you can experiment with to get the desired look.

A wet rag and baking soda, talc, comet cleanser, lime, etc. will also work. Use a dash of dish soap in your water.

All clear coatings are originally a gloss finish. Sheen is reduced by the addition of a flatting agent which can be purchased at a good professional paint supplier. Experimentation will allow determination of what you desire.

I was once building steel (raw iron) furniture for just that look. I had huge problems and ended up applying a coat of hot wax with a bunsen burner. Polished after wards but the process had to be reapplied if certain parts were won or touched more often.

Not sure what your application is so I could be right off the mark.

Good luck, Ky.

Are you referring to patina?

Well, there is a range where patina and just plain old rust on cor-ten overlap, but I would say no... what I'm talking about is just rust; in the manner that cor-ten is known for.

I use this stuff on lacquer finishes before refinishing, if it works on clear coat, it'll make it really easy. Home depot has it.

http://www.wmbarr.com/product.aspx?catid=32&prodid=91

Get your automotive clear coat paint and ask the store to add flattener to it. This with make it like a flat paint.

if you sand the paint or scuff it in anyway you won't be able to 'see' through it.

I was under the impression that COR-TEN had something in its metallurgy that made it self sealing once the corrosion had progressed to a certain point. Perhaps that characteristic only holds under a limited set of atmospheric/climatic conditions.

I note as a resident of the Mediterrean transitioning to Desert climate of the American West that even ordinary steels and cast irons seem to rust to a certain point and then remain unchanged for many years thereafter. Perhaps this is the nature of COR-TEN alloys albeit with some shift in the threshold of exposure to atmosperic humidity. And that thereby suggests an exposure point at which sealants become a logical solution to preservation of a particular appearance of the rusted surface.

You metallurgist types out there......... Any further comments on this?

Ed Weldon

Not sure I understand what you are attempting to do. Cor-Ten is a "weathering" steel which means it will form an adherent rust layer and then it will stop rusting anymore, unlike conventional steel which will continue to rust until it has rusted completely away. the operative word here is "adherent". the outer layer of rust is it's own sealant, protecting the steel from any further corrosion. Conventional steel when it transforms to rust expands which tends to pull the rust away from the underlying surface, but COR-TEN changes to a different kind of rust which is closer to the size of the original steel was so it sticks instead of peeling off, acting as a shield to any further corrosion. This is why it is used for bridges and such that are not easy to paint or maintain. coating it with anything will probably result in corrosion cells forming anywhere there are pinholes or uncoated areas leading to pits forming. IF you can ensure that it is completely covered with whatever coating you choose, then there ARE matte and satin clear urethane coatings that may serve your purpose.

That looks like some good stuff!

Guest is right that there are flattening agents available which will help knock down sheen, I don't know if you can add so much to bring high gloss down to matte without affecting performance.

Guest is wrong about not being able to see through a buffed surface. The wipe on deglosser that I mentioned works well.

Cor-Ten is a specialty steel that can be used in exposed areas and acts similar to aluminum which oxidizes readily. Once the initial layer has been formed, it becomes impervious to future corrosion. That is why it is used for statues and decorative objects. I'm not too sure of it Structural Properties, but as a previous contributor said it is used for bridges at times. Why try to beat a good thing with a coat of paint? Sounds like to much maintenance. Polyurethane based paints are best for corrosion prevention, but work well with a primer for best durability of adhesion. That would defeat the visual aspect that you were trying to impart. How important is it to stay a static image. Rust will not impair this steel, but maybe uniformity of color is important to you? This steel will also impart a patina which has a very unique appearance, and you may like it, it may grow on you. Rust away, its natural! Just that it doesn't harm the product in this century. Will this peace of art be meant to last into the next millennia?

Common shipment containers have wax what says "repair only with corten steel" and that is painted with epoxi paint i guess or polyurethane paint.Really i dont know, but may be you should ask how cont.manuf.or remakers do that.-

Nearly 20 years ago, I was involved in the construction of several extensive soldier beam and precast panel retaining walls. On account of aesthetic concerns, the beams, both "H"- and "WF"-section, were of COR-TEN steel. During the installation process, it was noted that there were irregular areas of mill scale that would take much longer to erode, resulting in a blotchy appearance as the rust layer (patina) would develop.

The decision was made to sand-blast all of the exposed faces prior to installing the precast panels. That activity provided a uniform "white metal" surface that could corrode uniformly. Within a few months, the surfaces were beginning to get the plum-colored patina that is characteristic of COR-TEN steel. During the ensuing years, the corrosion has reached the point that it is stable and the surfaces are very attractive and uniformly colored. The only modification we had to make, after observation, was to seal the precast panels to avoid rust stains along their interface with the soldier beams.

Based upon my understanding of the material characteristics of COR-TEN steel, along with my experience using it, I would suggest that you try the sand-blasting technique and then allow the material to do what it is designed to do without trying to coat it with anything. I have observed many bridge beams, guardrails, sculptures, and other structures that purposely utilized COR-TEN steel to provide a maintenance-free, attractive surface finish.

any marine paint used in shipyards to paint hulls would do well!

Out of Box Experience the US Steel building in Pittsburgh is housed in Cor-ten steel. The finish has aged quite nicely in Pittsburgh (although the sidewalks have been stained by the aging). The US Steel building is now known as the UMPC building. Google US Steel building-see some of info that comes up including how to contact US Steel in Pgh or Birmingham AL.

Thank you roadapple. Yes, I'm aware of UMPC building. Actually I'm quite familiar with all the properties and alleged properties of cor-ten. I've used it quite a bit over the years. Just not with the particular requirements that this project demands. It's my personal conclusion that cor-ten does not truly, in literal terms, "seal" itself. But in relative terms, it does. Relative to other steels, for instance.

But I digress. I need my steel to have a transparent coating on it, so that none of the rust rubs off when it's touched, or runs off when it's rained on. I also need to rust it immediately with the acid solution... as opposed to letting nature take its course... and then stop the process at the exact moment, and "look", that I require.

I think I've got some good ideas to try now.

Thank you all for the wide range of suggestions. Some good stuff here. But I have to say that as the posts progress, many of you have lost sight of the original requirements that I must maintain. Namely:

• Matte or satin type finish (not glossy)
• Weather-proof (not water based)
• Durable to manual handling (will not rub off if you sit on it, lean on it or rub your hand across it)
• **And of course, from context you can surmise that it must be a transparent coating

I find the POR15 suggestion, by BigPete, particularly intrigueing. Sounds like that may be just the ticket, if I can find it.

Thanx again.

Ah... I now see that the POR-15 product is a high gloss. That won't work for me. But perhaps with a buffing...

... or adding a flattening agent as was suggested.

... or the automotive clear coat that was suggested

I've got some testing to do.

First, read about stainless steels and the difference between 302, 304, 316 and 316L. Second, you will read that stainless has a "rust" capability that is really not "rust". Please struggle to understand this characteristic. Third, understand the result of oxygen and and the lack of oxygen and water entrapment without oxygen in crevice corrosion. Fourth, can you draw a similarity in the protective oxide layer to Corten? Fifth, in my opinion, the idea of a sealer (even if it lasts 50 years) is antithetical to the desired result. Sooner or later the work will need a resurface. Who will know how, will the paint still be available and are you going to make more of these over fifty years? Just a feeling, make the piece "work", let it age in one area of the country and let other pieces age in other areas. Wear and tear will buff it and the local environments will make each identical piece have a radical difference in finish. A Denver piece will appear very different than a Saint Augustine piece. The "paint" is a cloak that impedes the nature of the material to imprint and record its living environment, for those from other environments to see.

"Please struggle to understand this characteristic."

"antiethical" ?

What the hell? Are you lecturing me and scolding me, regarding what I want and need for this project?

You have no idea how far off-base you are. And if you were worth my time, I might try to explain it to you. All of your absurd assumptions regarding what I am doing and needing, are ridiculous; and quite wrong.

Don't be a hater. It's very sad. Especially an arrogant one who doesn't know what he's talking about.

On a lighter note... everyone else... thank you very much for all your ideas.

Yes as noted the glisten works for a particular reason, it is a humidity cure item, which is why when you paint over rust in general, it flakes off, this is because of the humidity level in the air when painting -rust absorbs moisture- so in effect you are painting wet metal- humidity cure paints use the moisture to set or dry - however have note for others considering this effect -it will not work with flaking rust due to the lack of sealant contact in the layers and the oxygen and moisture content within the layers.

to the other component of the question, the acid -wash well with water and then use actetone in a spray bottle, this is to remove any fat or oils from your hands touching it, rinse with water and allow to dry or dry in a heated room like a paint booth- also a note for other considering the effect, the copper will slow the rust down not speed it up - rust converters are made from a copper acid base. Copper is something I assume you read on a patina site, this is designed to create a green effect when combined with acid, the resulting look on steel is meant to be like old bronze, if the item in question would never have been bronze, the green will look out of place- additionally it is hard to rinse without washing the patina back off. When i say out of place, I mean when painting a marble effect it only works on big chunky items that could be marble, painting the effect on a half inch board over a fire place would look silly, so too bronze was rarely ever used in sheet form except for boiling pots, sheilds and chariot surrounds.

Hope this helps

Archie

Enerventure

This is good stuff Archie.

Humidity Cure item, eh? Okay, you've put a name to a theory I've had. That makes some things a bit clearer now.

As far as the copper... honestly, I'm not sure why it's in the solution. That's what they have been using here. My job consists of figuring out unusual engineering problems that have stumped those that started the projects; and it covers all diciplines. At the moment, it happens to be this issue of finding an appropriate seal for treated Cor-Ten. I use all tools at my disposal, which occasionally includes asking my friends here on CR4 for their opinions. It's always great to find experts in very specific areas that I'm working on. At the moment, you seem to be one of those. I appreciate you sharing what you know, with me.

This particular item is a very large panel, that is likely to have people in contact with it. We're trying to make it look attractive... or at least interesting... in an old, ramdom, rusted sort of way. But we can't have it making peoples hands or clothes red... nor staining any concrete... hence, the sealant. The non-gloss, or matte, finish is what is being requested.

Copper is in COR-TEN, it is one of the elements that make it a weathering steel. there are several weathering steels and the more copper they contain, the more "weathering" they are.

I have built a fountain out of Corten 3/16 thick which as four bowls that spill into one another. The Corten bulids up a thick orange rust which discolors the water. Even a sample bowl that has been out in the weather ( southern CA) and has developed an even scale of rust will ooze orange rust when filled with water. Have you found a clearsealer solution to your problem? I am thinking that I may just have to sandblast and powder coat. Will any clear really stick to the rust? It won't work to have flakes of some 2 part polyurethane coming off in a couple of years. Thanks in advance for any advise.

I have built a fountain out of Corten 3/16 thick which as four bowls that spill into one another. The Corten bulids up a thick orange rust which discolors the water. Even a sample bowl that has been out in the weather ( southern CA) and has developed an even scale of rust will ooze orange rust when filled with water. Have you found a clearsealer solution to your problem? I am thinking that I may just have to sandblast and powder coat. Will any clear really stick to the rust? It won't work to have flakes of some 2 part polyurethane coming off in a couple of years. Thanks in advance for any advise.

I only know of gloss, but it will protect the surface for ten years or so. It's water clear.

Stu.